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South Australia worms, flies and lice update - March 2016

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides


Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (trengovet@icloud.com)

The typically atypical start to the year continues with sporadic rainfall received across the State in the past 2 weeks….most notably 20 mm in 30 minutes to finish the Clipsal 500 car race in Adelaide on 6 March. This rain, as a follow up to that received in late January / early February, has produced a significant green pick in parts of the upper SE, mid north, Adelaide hills, KI and the three Peninsulas.

Recent WEC monitoring appears not to have been influenced by the summer rain. Approximately 40% of egg counts from the mid north to the upper SE have exceeded 100 eggs per gram (epg), potentially warranting a drench. One count of 1000 was indicative of Haemonchus (barber’s pole infection) in dry Merino hoggets, while associated pregnant ewes had counts of 175–225 epg. This highlights the variable nature of haemonchus infection related mostly to lighter soils and sufficient summer rain to allow moisture to persist for the worm to infest emerging pasture and infect grazing animals. These circumstances are usually unique to particular areas on a property and so other paddocks and mobs remain a low risk to Haemonchosis.

Monitoring several mobs at this time of year is invaluable in the interest of minimising drenching and the development of drench resistance. A drench in autumn is vital if egg counts indicate a developing worm burden, but otherwise drenching is discouraged as it is undesirable to expose the worm population in the gut to chemicals unless entirely necessary.  The presence of a short green pick increases the risk of developing a worm infestation, but monitoring faecal counts 3-4 weeks after grazing the green feed is the most effective means to check whether worms are present.

Rain up to 70mm on the EP in the last fortnight is likely to have produced conditions favourable to flystrike. Frequent close checking of mobs with sufficient wool length and no fly protection is essential to prevent losses from this ailment. Fly resistance to chemicals is not as much a concern as worm chemical resistance, but it is still important to also check mobs given preventative treatments rather than assume the chemical has remained highly effective.